The present invention relates to equipment for the drying of metal turnings or scrap prior to such being used in melting furnaces.
Metal turnings, both ferrous and non-ferrous, must be dried in order to remove their liquid content before they are used in melting furnaces. In fact turnings from machine tools always contain liquid of the order of 3-5% on average and comprising the residues of cutting oils or coolants, solvents, additives, water, etc. If these liquids are not removed in advance they tend to cause agglomerations or clumping when the turnings are loaded into melting furnaces and to form compact layers on the surface of the molten metal. The gases which are produced by the presence of such liquids also tend to give rise to explosions, flare-ups and toxic fumes, and when in contact with the metal they give rise to the formation of oxides and slag with a consequent loss of metal.
It has been found that the loss of metal on melting is directly proportional to the liquid content of the initial turnings. An investigation based on many fusion tests with brass turnings has shown that there is a loss of about 30% of molten metal when the initial turnings have a high liquid content, against a loss of 2-3% when dried turnings are used. Various apparatus have already been proposed in which the material which is to be dried is passed into a drier and heated directly by a heat source which burns a combustible gas, and these apparatus for the drying of material such as turnings, in addition to processing involving washing with solvents, centrifugation, etc., have nevertheless in the main proved themselves to be sources of waste and pollution. When the material is heated the liquids contained within it evaporate and therefore form vapors. Some of these burn in the drier when in contact with the flames used to heat the material while the remainder are collected and passed out of the drier where they are normally burnt in another afterburner using another fuel.
Units of this type are rather complex and cumbersome and involve both a high energy consumption, and thus high operating costs, partly because they are not able to utilize the calorific content of the vapors produced, which is high, and also require apparatus for cooling and filtering of the fumes before they are discharged to the atmosphere in order to prevent pollution. The afterburner also frequenly clogs up as a result of the dust carried by the fumes and requires periodical shut-downs to permit cleaning to be effected.
To be specific, apparatus of the known type are, in addition to having inconveniences and disadavantages in operation, rather complex and cumbersome and normally require special foundations or in any event require masonry structures which place a large burden on the costs of the units in addition to high operating costs.